In this letter, George Witt made several misleading and incorrect allegations concerning the reliability of the global temperature record, as well as the credibility of groups who produce them. I do share Witt's concern about the rapid decline of monitoring sites used to generate these global analyses, especially given that the Canadian Arctic is among the fastest warming regions of the world.

And it is a mystery why so few of the available Canadian stations make it into the Global Historical Climate Network (GHCN) database used by NASA. Regardless, the Clear Climate Code team (Nick Barnes) has demonstrated that the exclusion of monitoring sites from Canada has virtually no impact on temperature trends for regions of the globe north of 64 N. Their analysis showed that region is warming at over 5 C per century (30-year trend), compared to the long-term global warming trend near 2 C per century.

Witt refers to a recent study which suggests that inappropriate station location makes U.S. temperature trends unreliable. However, a peer-reviewed paper (Menne et al. 2010) has shown that the temperature trend over the U.S. derived using all data is almost identical to the trend derived using a subset of data with ideally located stations. In fact, including the "problem" sites produces a lower rate of warming. Menne et al. concluded that "we find no evidence that the U.S. average temperatures are inflated due to poor station citing."

In 2009, NASA predicted that 2010, in the absence of a major tropical volcanic eruption or onset of a strong La Nina, would likely be the warmest year on record.

NASA data up to this November indicate that, despite the sun only recently emerging from a prolonged solar minimum and despite the onset a of strong La Nina event the past summer (which cools global temperatures slightly), 2010 will indeed probably be the warmest year on record.

Witt claims that NASA is refusing to release its "raw" data. I'm not sure what he means by "raw" data. Most of the data (both adjusted and unadjusted) are freely available on the Internet, and in the past year, several individuals and groups have, with very little effort, reproduced and validated the NASA GISTEMP and HadCRUT global data sets using information available on the Internet. Nor has any of the original data been lost for good, as Witt suggests. Those temperature data still reside with the original owners and proprietors of the data.

For all their limitations, the global temperature records are robust.

And multiple, independent lines of evidence all corroborate the fact that the planet is accumulating energy and warming.

The long-term rate of warming from satellite data is consistent with the surface temperature records; so is the warming evident in weather balloon data and warming of the oceans, not to mention the loss of ice from glaciers around the globe and the rapid loss of Arctic sea ice volume. The warming is hardly surprising given that we humans have, in an incredibly short time, increased CO2 to its highest levels in 800,000 years and likely even the past 15 million years.

One last note about the cold weather affecting portions of Europe. To place that in context, NASA just released data showing that, globally, November 2010 was the warmest on record -- which is not surprising given that Europe covers only two per cent of the planet.

Climate scientists have warned that by rapidly warming the planet, we are loading the dice to favour more frequent extreme weather events. We are essentially disrupting the climate system. It is unfortunate that some of us continue to ignore the myriad of warning signs happening before our very eyes.

Graham Thomson takes a reader to task for the sin of relying on his Edmonton weather observations and extrapolating these to form an opinion on global warming.

Thomson calls this approach illogical and compares it to "passing judgment on global warming by glancing at their backyard thermometer."

Thomson then goes on to cite his evidence for global warming by glancing at his own backyard thermometer, albeit a somewhat larger backyard, but a backyard nonetheless.

He offers such examples as forest fires in Russia and B.C., drought in Africa and on the Canadian prairies, and the lack of snow for the recent Olympics. However, this appears to be to some extent a case of backyard cherry picking, as he fails to mention that the drought in the southern prairies ended this year with such cool wet weather that many crops were destroyed or badly damaged.

Further, he does not mention the record cold weather and snow that has affected the UK, the coldest in 100 years, and Europe, nor the record snowfall affecting Ontario and Quebec and the northeast U.S.

Thomson does however quote David Phillips, of Environment Canada, as stating that "this year will clearly be the warmest year on record in Canada" -- another big backyard.

Phillips is a contributor to the NASA GISS weather monitoring agency.

NASA came out last week, well before year end, with its forecast that 2010 will be the warmest year on record. Interestingly, this early announcement coincides with the Global Warming conference being held in Cancun, Mexico, which incidentally is experiencing record cold temperatures.

When NASA came out with their results last year, it was reported in The Journal that only 30 odd sites were used to determine Canada's temperature, only one of which was in the Arctic. At that time Environment Canada raised its concern that so few monitoring sites selected from Canada may understate global warming.

Temperature records are a hotly debated subject. Previous to the 1960s there were over 7,000 world surface temperature monitoring sites; today there are less than 3,000, which makes it very difficult to accurately compare current with historical results.

A recent U.S. study of its surface temperature monitoring sites showed that more than 85 per cent were unreliable for reasons of location, maintenance and accuracy.

The U.S. sites are reported to be the world's best. As a result of problems with the monitoring sites, scientists massage the readings to adjust for abnormal readings and they also select only certain preferred sites to use for their annual reporting.

Consequently the original raw data that establishes the base for determining such things as the warmest year is greatly corrupted.

The University of East Anglia Climate Unit of "Climategate" fame refused to release its raw data for two years before admitting that it no longer had the raw data and could not reproduce it.

Currently, NASA is refusing to release its raw data, which has prompted the introduction of a U.S. Senate bill that if passed will force NASA to release its information.

So, in the absence of reliable raw temperature data, and the lack of information from which other scientists can replicate or falsify the processes used to determine the extent of or lack of warming, we are left with Thomson's "illogical approach" of glancing at our "backyard thermometer" as the best way to assess global warming.